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Achintha, Paththini Marakkala Mithila. "Fracture analysis of debonding mechanism for FRP plates." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/240575.
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Inevitable flaws in the concrete-FRP interface govern plate debonding, and are not amenable to finite element analysis because the models require far more detail than will ever be available for the interface. This thesis describes a global-energy-balance based fracture-mechanics model for the debonding mechanism of externally bonded FRP plates attached to concrete beams. The model investigates the possible propagation of an existing interface crack by considering the energy balance of the beam during a small potential crack extension. The crack will extend if the energy release rate is greater than the interface fracture energy. Despite the fact that the crack-tip stress field is not amenable to precise analysis, its influence on the energy balance of the beam is insignificant because of the small volume of the "uncertain zone", whereas the crack tip stress field would solely govern an analysis based on linear elastic fracture mechanics. The plate end and the locations where the widening of flexural and flexural/shear cracks cause interface flaws are the most likely locations for the initiation of debonding. The model analyses debonding that initiates from either location. With the small extension of the interface crack the compatibility between the beam and the FRP alters, consequently causing changes in the stress states, and hence the energy states, of zones in the vicinity of the crack. The change in energy state of a beam section upon interface crack extension is determined from a modified version of Branson's model. The strain state when the FRP is fully or partly debonded needs to be considered. The mechanics of stress transfer from the concrete to the FRP differs from that with conventional steel reinforcing bars for which the accuracy of the original Branson's model was validated. So, the moment-curvature model considers the force in the FRP as an external compressive force on the concrete beam section; the separation of the effects of the axial force and the moment is achieved by defining an equivalent centroid. Debonding will propagate in whichever of the concrete, adhesive, or at an interface that provides the least resistance; thus, the interface fracture energy is that of the weakest phase. Experimental observations confirm that the concrete substrate just above the interface is most likely to fail, in particular when the FRP manufacturer-recommended adhesives are used with appropriate curing procedures. Fracture energy of concrete is determined from Hillerborg's cohesive-crack-model-based experimental and approximate theoretical models. Premature debonding propagation within the adhesive layer can also be analysed but the knowledge of that fracture energy is required. The energy release rate is calculated for assumed interface crack lengths and locations, from which the critical state is determined when it equals the interface fracture energy. Comparisons with test data reported in the literature demonstrate that the model is accurate for all modes of plate debonding. The analysis gives the critical plate curtailment location and the critical crack length which trigger debonding at the plate end and in the high moment zone respectively. The model allows for the inclusion of all properties of the concrete beam, adhesive, FRP and the loading arrangement and hence can be used as an optimisation tool in design. The model also provides a framework for the design of more complex real -life applications, and highlights subjects that require further research.
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Zhu, Wenzhong. "Effect of ageing on durability and micro-fracture mechanism of fibre reinforced cement composites." Thesis, University of the West of Scotland, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259743.
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Bourga, Renaud. "The mechanism of leak-before-break fracture and its application in engineering critical assessment." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/15289.
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This thesis investigated the different aspects and mechanisms of leak-before-break (LBB) assessment. The main objective was to improve the understanding of the transition between surface and through wall defects. While existing procedures generally idealise the through-wall crack into a rectangular shape, in reality a crack propagates with a shape depending on the loading. Comparison between the related solutions from established procedures have been undertaken. The apparent variation depending on the solutions used in the assessment has been highlighted. Two different methodologies have been employed to investigate the transition of flaw: (i) non-ideal through-wall and (ii) surface-breaking flaw propagation. The first approach consists of numerical models of non-idealised flaws in order to assess the effect on LBB parameters. For the second approach, experiments have been first carried out to visualise the shape of defect growths. To further study surface-breaking flaws, both experimental and numerical studies were performed. Fatigue tests on deeply notched plates with two crack aspect ratios were carried out. Strain evolutions on the back surface were recorded along the axes parallel and perpendicular to the crack. Numerical models have been prepared to investigate a larger scope. Behaviour of growing surface-breaking defects was examined. Based on the work conducted in this research, the major findings can be summarised as follows: - The existing solutions to carry out a LBB assessment using available procedures were reviewed and discussed. For axial flaws, SIF solutions were found similar and in good agreement with FEA values. Reference stress solutions showed significant difference between BS 7910 and API 579-1/ASME FFS-1. When compared to experimental data, API's solutions were able to distinguish between leak and break cases. - Flaw geometry assumption for through-wall crack yet to become idealised did not always reflect the actual behaviour, especially for COA calculation. In this case, FEA can be used as a good predictive tool for LBB to estimate margins when assessing leak rate. - The experiment using metallic specimens showed that high stress/strain on back surface would provide a good estimate of the crack propagation as it approached break-through. This offers a more accurate monitoring mechanism. Strain-mapping devices such as gauges could be used.
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Izadian, Mohammad Hossein. "Understanding the mechanism & effects of stent fracture : a combined experimental & finite element analysis." Thesis, University of Hull, 2018. http://hydra.hull.ac.uk/resources/hull:17250.
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Atherosclerosis is a common heart disease, categorised by a build-up of fatty substances (plaque) in the inner surface of the coronary arteries and causing obstruction to the blood flow to vital organs and other parts of body. Over time, the arteries become narrowed which can lead to serious complications such as angina, heart attack, and stroke. There are several treatments to slow down the progress and reduce the risk, including medication and medical procedures. Percutaneous coronary intervention (PCI) is a non-surgical procedure which reopens blocked arteries and restores the blood flow. In some cases the PCI involves a tiny mesh tube known as a stent, which is placed in the narrowed artery to widen the lumen, support the vessel wall and prevent restenosis. Whilst this is generally successful procedure, stents might cause further problems such as stent fracture, in-stent restenosis, and stent thrombosis. Stent fracture is known to be associated with a number of factors; stent length, stent overlap, vessel tortuosity, degree of calcification of lesions, stent design, and the conditions under which the stent operates. The first part of this thesis presents a design-independent finite element analysis evaluation of the relative stresses induced in a coronary stent when placed in an angulated vessel geometry. This was achieved by idealising the stent to a thin tube, with the structural modulus of the tube representing that of a stent-like structure (this could be adapted for different types of stent structure). The artery and stent were then subjected to a displacement representing a bending movement of 20˚. Furthermore, various artery angles were modelled from 30˚ to 90˚ and each time the angle was transformed in 10˚. This series of finite element analyses computed the stress distribution associated with the displacement, hence quantifying the relationship between the vessel angle and the stress when considering the "hinge-type" movement that the vessel will undergo with each heartbeat. This constant repetitive loading constitutes the most severe mechanical loading that the stent will undergo, which far exceeds the radial expansion/contraction systolic/diastolic of the vessel or any torsional effects. It was observed that changes in stresses within the stent model are directly proportional to the vessel angulation, which stresses increased when the vessel angles became more severe. Furthermore, the bending region where was associated with the hinge-type movement experienced higher amounts of stress in the idealised stent model, and severe vessel angle caused a larger area undergo higher stress. The values increase at a greater rate once an angle of 75 degree has been exceeded, which agrees with clinical observation. Also areas of high stress corresponded to areas where fractures are seen clinically. The second part involved the mechanical testing of 9 samples of four different stent designs; Muilti-Link Vision®, PRO-Kinetic Energy, BioMatrix NeoFlexTM and Promus PREMIER. Stents deployed at nominal pressure into physiological mock artery at initial angle of 90˚, were then subjected to a 20˚ continuous repetitive hinge-type movement, at a rate of approximately 1100rpm (cycles per minute). By 300 million cycles fractures were identified in 7 stents, and are limited to only the Biomatrix design (34.67±28.78 million cycles), exhibiting between one and four strut fractures. Fractures were first seen to occur at 13.5 million cycles, where fractures were observed in 2 stents. All fractures were seen to occur at the ring linker parts of the stent and in the areas which would undergo the most severe tensile and compressive loading. This study shows that artery angulation has a significant impact on the stent stress, and more tortuous vessel increases the risk of stent fracture. Also in vitro experimental work illustrates that stent material and structure play an important role in stent flexibility.
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Nagl, Michael Martin. "Identification of the mechanism of oxide scale fracture, and its correlation with strain using acoustic emission." Thesis, University of South Wales, 1992. https://pure.southwales.ac.uk/en/studentthesis/identification-of-the-mechanism-of-oxide-scale-fracture-and-its-correlation-with-strain-using-acoustic-emission(60f7dec2-bf42-4f44-86f7-b216a1adc662).html.
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Thermally formed oxides scales can protect metals from aggressive environments at high temperatures. However the barrier function is destroyed when the oxide fails. Therefore a new 4-point bend test technique has been developed to measure the failure strains and to study the failure mechanisms of brittle layers in tension and compression. Tests were made with iron oxide and nickel oxide at room temperature and 550 or 900 °C, respectively, using strain rates of 10~* and 10"5 s"1 . Brittle lacquer was used as a model layer. Acoustic emission (AE) was employed to monitor and interpret failure mechanisms together with post test metallography. Equi-distant cracks were formed during failure in tension. Further cracking was affected by elastic and plastic stress relaxation processes, and interface delamination only started after these processes were exhausted. The crack spacing increased with oxide thickness and the results indicated that plastic relaxation processes were dominant at growth temperature conditions. The shear strength of the interface was lower at growth temperature. Shear failure within the layer was found in NiO and brittle lacquer when tested in compression. Failure in iron oxide under compression always started at the interface. The failure mechanism and initiation in compression was determined by the relative shear strength of interface, the shear strength of the layer and the buckling stability of the layer. However, spallation always required crack growth at the interface. Measured failure strains in tension and compression agreed well with the predictions of a model incorporating the fracture mechanics condition for tensile cracking or interface crack growth respectively and factors like residual strains, oxide creep and lateral oxide growth which accounted for the behaviour of a thin growing scale on a thick substrate. The critical fracture mechanics parameter in tension was the composite void size. A K1C value of ~ 1.1 MN nv3/2 was obtained for iron oxide for room temperature and 550 °C. Values of 0.41 and -1.61 MN m3/2 were found for NiO at room temperature and at 900 °C, respectively. The residual growth stresses in iron oxide were determined as approximately zero and the cooling strain from 550 °C was -0.05 - 0.06%. The residual stresses in NiO were -175 MPa at room temperature. The strain energy release rate for interfacial failure in iron oxide was 27 J m-2 and the fracture surface energies were 3.4 and 0.8 J m-2 for iron and nickel oxide, respectively. AE was a useful tool for explaining the failure mechanisms and a numerical analysis showed a slight difference in the AE signal released during tensile and compressive failure.
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Lacroix, Gauthier. "On the relationships between microstructure and mechanical properties of TRIP-assisted multiphase steels : strength, ductility, fracture and fatigue." Université catholique de Louvain, 2007. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-11302007-114213/.
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In the context of sustainable development, steelmakers and automotive manufacturers decided for some years now to join their efforts to promote the development and use of advanced high strength steels such as the present TRIP steels in order to reduce the fuel consumption and emission of greenhouse gas. These multiphase steels contain some retained austenite, a ductile phase that can transform into hard and brittle martensite during a mechanical solicitation. One the one hand, this transformation improves the mechanical properties during plasticity by bringing about an additional work-hardening. On the other hand, the appearence of a hard and brittle phase can give rise to premature cracking after necking. Knowing the good influence of martensitic transformation on the work-hardening, this Thesis starts with the characterisation of the relationship between transformation rates and testing conditions. It appears that, for each testing condition, there is an optimum austenite stability that leads to a maximum uniform strain. After necking under monotonic loading conditions, the damage mechanisms that takes place in these steels has been characterised. It can be concluded that the TRIP-aided steels that present low or moderate austenite stability behave exactly like Dual-Phase steels, in which martensite replaces retained austenite. However, a very stable retained austenite brings about a significant toughness improvement by providing an additional work-hardening contribution in the necking zone. The mechanical behaviour of these steels has also been characterised under cyclic loading conditions. The results indicate that, for particular loading conditions (i.e. low load levels), the martensitic transformation improves the fatigue properties.
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Lu, Xuekun. "Characterisation of the anisotropic fracture toughness and crack-tip shielding mechanisms in elephant dentin." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/characterisation-of-the-anisotropic-fracture-toughness-and-cracktip-shielding-mechanisms-in-elephant-dentin(5f0a739b-e30a-401e-905a-b38e9224ac0a).html.
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Teeth trauma has become one of the most serious physical problems that people are suffering from in the past years. Early diagnosis and management are desperately needed to improve tooth survival, functionality and avoid the tooth loss. However, the diagnosis of cracked tooth could be challenging due to the small size of the crack. Therefore, a mechanics understanding of the tooth fracture is demanding from the perspective of developing a framework for failure prediction in clinical research and bio-mimetic restorative materials. This study focuses on characterising the anisotropic fracture behaviour and the crack shielding mechanisms in elephant dentin. This is often used as a structural analogue for human dentin due to the similarities in microstructure and chemical composition, in order to avoid the test-piece size restrictions, given the larger size of ivory than human teeth. Compact tension test-pieces were extracted from different locations on the ivory tusk so as to have different crack growth directions relative to the microstructure to inspect the fracture anisotropies. The fracture toughness as a function of the crack extension was assessed in terms of fracture resistance curves (R-curve). The accumulative crack-tip strain fields were also measured for the first time in dentin using digital image correlation technique (DIC) to investigate the capability of crack-tip elastic/plastic deformation before material failure. Investigation of crack morphologies, the interaction between crack and the microstructures, the fracture surfaces using both 2-D and 3-D techniques could provide with insights into extrinsic shielding mechanisms. Surface and volume crack opening displacement (COD) were measured for the first time optically and by X-ray computed tomography to investigate the effect of extrinsic crack-tip shielding. The displacement fields around the crack-tip obtained by DIC were fitted using Westergaard’s analytical solution to extract the effective stress intensity factor, by comparing this to the applied load, the efficiency of the crack-tip shielding could be evaluated. A novel cohesive element model (traction-separation law) was then established based on the COD results to simulate the physical process of crack-tip shielding. It is the first time the cohesive model has been adapted to studying the direct crack behaviour measured by in-situ experiment to predict the crack growth. This model was then validated using the crack-tip strain field and R-curve obtained from the experiment measurement.
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Patel, Ammar Abbas. "Epoxy Adhesives: Formulation for Sustainability and Mechanism of Adhesion." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1573254388960149.
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Srivastava, Ankit. "Mechanics and Mechanisms of Creep and Ductile Fracture." Thesis, University of North Texas, 2013. https://digital.library.unt.edu/ark:/67531/metadc283799/.
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The main aim of this dissertation is to relate measurable and hopefully controllable features of a material's microstructure to its observed failure modes to provide a basis for designing better materials. The understanding of creep in materials used at high temperatures is of prime engineering importance. Single crystal Ni-based superalloys used in turbine aerofoils of jet engines are exposed to long dwell times at very high temperatures. In contrast to current theories, creep tests on Ni-based superalloy specimens have shown size dependent creep response termed as the thickness debit effect. To investigate the mechanism of the thickness debit effect, isothermal creep tests were performed on uncoated Ni-based single crystal superalloy sheet specimens with two thicknesses and under two test conditions: a low temperature high stress condition and a high temperature low stress condition. At the high temperature, surface oxidation induced microstructural changes near the free surface forming a layered microstructure. Finite element calculations showed that this layered microstructure gave rise to local changes in the stress state. The specimens also contained nonuniform distribution of initial voids formed during the solidification and homogenization processes. The experiments showed that porosity evolution could play a significant role in the thickness debit effect. This motivated a basic mechanics study of porosity evolution in single crystals subjected to creep for a range of stress states. The study was performed using three-dimensional finite deformation finite element analysis of unit cells containing a single initially spherical void in a single crystal matrix. The materials are characterized by a rate-dependent crystal plasticity constitutive relation accounting for both primary and secondary creep. The effect of initial void spacing and creep exponent was also explored. Based on the experimental observations and results of finite element calculations a quantitative mechanistic model is proposed that can account for both bulk and surface damage effects and assess their relative roles in the observed thickness debit effect. Another set of calculations aim at relating the crack growth resistance and fracture surface morphology to material microstructure for ductile structural metals. The process that governs the ductile fracture of structural materials at room temperature is one of nucleation, growth and coalescence of micron scale voids, and involves large plastic deformations. Experimental studies have shown that fracture surfaces in a wide variety of materials and under a wide variety of loading conditions have remarkable scaling properties. For thirty years, the hope to relate the statistical characterization of fracture surfaces to a measure of a material's crack growth resistance has remained unfulfilled. Only recently has the capability been developed to calculate sufficient amounts of three dimensional ductile crack growth in heterogeneous microstructures to obtain a statistical characterization of the predicted fracture surfaces. This development has enabled the exploration of the relation of both fracture toughness and fracture surface statistics to material properties and microstructure when the fracture mechanism is one of void nucleation, growth and coalescence. The relation of both toughness and the statistical properties of fracture surfaces in calculations of heterogeneous microstructures to various microstructural features is discussed and a remarkable correlation between fracture surface roughness and fracture toughness is shown for the first time.
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Davidson, Melissa Anne. "A Pharmacovigilance Approach for Assessing Cardiovascular, Osteological, and Carcinogenic Risk Associated with Thiazolidinedione Drugs Used in the Treatment of Type 2 Diabetes Mellitus." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38062.
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Diabetes is a chronic and debilitating disease that affects nearly half a billion people worldwide with the vast majority of diabetics suffering from Type 2 diabetes mellitus (T2DM), a disease characterized by insulin insensitivity that often requires pharmacotherapy to effectively maintain target blood sugar levels. The thiazolidinedione (TZD) class of drugs consists of oral hypoglycaemic agents used alone or in combination with other antidiabetic drugs to treat T2DM. The drugs within this class, which include rosiglitazone and pioglitazone, were originally heralded as providing novel first and second-line treatment of T2DM with glycaemic control and physiological effects comparable to, and in some cases, better than, first-line treatments such as metformin. However, over time they have also been associated with adverse cardiovascular, osteological, and carcinogenic effects in some, but not all clinical trials, observational studies, and meta-analyses. Given the conflicting evidence to date on the safety of TZD drugs, their role in the treatment of T2DM continues to be debated and epidemiological gaps remain. The objectives of this doctoral research are fourfold: 1) to conduct an in-depth review of the epidemiology of TZD pharmacotherapy including pharmacokinetics and modes of action, the results of previous studies investigating health risks and benefits associated with TZD treatment, and new and future uses for this class of drugs; 2) to determine whether diabetic patients treated with TZDs are at increased risk of adverse cardiovascular outcomes; 3) to assess whether TZD pharmacotherapy is associated with an increased risk of bone fractures and whether risks differ depending on fracture site and patient sex; and, 4) to investigate associations between TZD use and risk of bladder cancer. Specific research questions were investigated using nested case-control analyses designed to capture incident users of antidiabetic drugs and electronic health data from Cerner Health Facts®, an electronic medical record database that stores time-stamped patient records from more than 480 contributing hospitals throughout the United States. Findings from this work are reported in a series of manuscripts, including a published review paper. Key findings include: 1) TZD use was associated with an increased risk of incident myocardial infarction and congestive heart failure compared to never use of TZD drugs with a trend towards a potential early treatment effect within the first year of exposure to pioglitazone; 2) TZD use was associated with an increased risk of closed bone fractures among Type 2 diabetics with use of pioglitazone or rosiglitazone associated with an increased risk across multiple fracture sites in women, but only rosiglitazone use in men and only at peripheral fracture sites; 3) use of either pioglitazone or rosiglitazone were associated with an increased risk of incident bladder cancer compared to never users, however, a low number of bladder cancer cases resulted in underpowered analyses; and, 4) insulin use in a hospital setting may replace a patient's normal course of antidiabetic therapy which, when combined with other potential sources of bias in traditional nested case-control studies using hospital-based data, may lead to overestimation or underestimation of adverse health risks associated with non-insulin antidiabetic therapies. Although these findings warrant replication, the results of the research contained within this dissertation suggest that caution should be exercised when prescribing diabetic patients TZD drugs if they have cardiovascular, osteological, or carcinogenic risk factors. Additional pharmacovigilance studies should also continue to strive to better understand the health risks related to TZD therapy, especially as new therapeutic roles for TZDs in the prevention and treatment of some cancers, inflammatory diseases, and other conditions in non-diabetic populations are being explored.
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Gieseke, Brian G. "Mechanics and mechanisms of creep-fatigue crack growth in Cu-1 wt% Sb." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/19982.
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Druiff, Helen. "Micro-mechanisms of ductile fracture." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385328.
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Wang, Yaou. "Failure mechanism and reliability prediction for bonded layered structure due to cracks initiating at the interface." Columbus, Ohio : Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1236645979.
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Mansfield-Williams, H. D. "Mode 11 fracture mechanics in solid wood and fracture mechanics in laminated veneer lumber." Thesis, Brunel University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390815.
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Zhang, Guihua. "Development of numerical approaches to predict ductile and cleavage fracture of structural materials." Akron, OH : University of Akron, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1196174104.
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Dissertation (Ph. D.)--University of Akron, Dept. of Mechanical Engineering, 2007."December, 2007." Title from electronic dissertation title page (viewed 03/27/2008) Advisor, Xiaosheng Gao; Committee members, T.S. Srivatsan, Fred Choy, Wieslaw Binienda, Kevin Kreider; Department Chair, Celal Batur; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
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Denning, Shawn Patrick. "Fracture mechanics of sandwich structures." Thesis, Wichita State University, 2013. http://hdl.handle.net/10057/6809.
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Over the past few decades both the demand for knowledge as well an increase in the application of composite materials has boomed. This has led to an intensive focus by the research community to gather information and validate the use of such materials. Sandwich composites have been a particular interest and an intense demand for further understanding was sparked by the catastrophic rudder failure of Air Transat 961. This thesis focuses on understanding fracture mechanics and damage tolerance within sandwich composites. Facesheet disbond has severe impacts on the material systems strength and stiffness, and large disbonds can often lead to catastrophic component failure. Understanding how these disbonds grow is paramount to recognizing the limitations of sandwich composites.
This thesis has several objectives. First, determine the fracture toughness of various sandwich composite material systems under going quasi-static loading. Second, determine how variations within the material systems such as facesheet thickness, core type, cell size and core density effect the results. Third, determine how the failure modes such as adhesive, pullout and core alter the results. Fourth, determine how fluid ingression effects fracture toughness. Fifth, provide baseline data for further testing and modeling.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering
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Matthews, C. "Fracture mechanics of volcanic eruptions." Thesis, University College London (University of London), 2009. http://discovery.ucl.ac.uk/16280/.
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Seismology is a key tool in the forecasting of volcanic eruptions. The onset of an eruption is often preceded and accompanied by an increase in local seismic activity, driven by fracturing within the edifice. For closed systems, with a repose interval of the order of a century or more, this fracturing must occur in order to create a pathway for the magma to reach the surface. Time-to-failure forecasting models have been shown to be consistent with seismic acceleration patterns prior to eruptions at volcanoes in subduction zone settings. The aim of this research is to investigate the patterns in seismic activity produced by a failure model based on fundamental fracture mechanics, applied to a volcanic setting. In addition to the time series of earthquake activity, statistical measures such as seismic b-value are also analysed and compared with corresponding data from the field and laboratory studies. A greater understanding of the physical factors controlling fracture development and volcano-tectonic activity is required to enhance our forecasting capability. The one dimensional, fracture mechanics grid model developed in this work is consistent with the theory of growth and coalescence of multi-scale fractures as a controlling factor on magma ascent. The multi-scale fracture model predicts an initial exponential increase in the rate of seismicity, progressing to a hyperbolic increase that leads to eruption. The proposed model is run with variations in material and load properties, and produces exponential accelerations in activity with further development to a hyperbolic increase in some instances. In particular, the model reproduces patterns of acceleration in seismicity observed prior to eruptions at Mt. Pinatubo (1991) and Soufriere Hills (1995). The emergence of hyperbolic activity is associated with a mechanism of crack growth dominated by interaction and coalescence of neighbouring cracks, again consistent with the multi-scale fracture model. The model can also produce increasing sequences of activity that do not culminate in an eruption; an occurrence often observed in the field. Scaling properties of propagating fractures are also considered. The seismic bvalue reaches a minimum at the time of failure, similar to observations from the field and measurements of acoustic emissions in the laboratory. Similarly, the fractal dimension describing the fracture magnitude distribution follows trends consistent with other observations for failing materials. The spatial distribution of activity in the model emerges as a fractal distribution, even with an initially random location of fractures along the grid. Significant shifts in the temporal or spatial scaling parameters have been proposed as an indication of change in controlling factors on a volcanic system, and therefore represent a relatively unexplored approach in the art of eruption forecasting.
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MacLennan, Iain James. "Two parameter engineering fracture mechanics." Thesis, University of Glasgow, 1996. http://theses.gla.ac.uk/6756/.
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The object of this work was to investigate and expand on previously carried out research into elastic-plastic crack tip fields using the first two terms of the Williams expansion to characterise the degree of crack tip constraint. As a precursor to this research a history of fracture mechanics is also presented. In the present work crack tip fields in small scale yielding have been detennined using modified boundary layer formulations in an attempt to model the influence of the second order term of the Williams expansion, the T -stress. The prime object of this thesis was to investigate and expand on previously carried out research into a two parameter characterisation of elastic-plastic crack tip fields using the second parameter of the Williams expansion(T), which attempts to characterise the degree of crack tip constraint. Modified Boundary Layer formulations in conditions of plane strain were implemented to derive a suitable reference solutions, against which the effects of out of plane strains can be compared and the validity of presently established reference fields can be gauged. The effect of out of plane non-singular stress, S, on the crack tip stress field were also considered, where constraint was largely determined by T. A wide range of analyses have been carried out, from the microstructural scale to complete engineering components in an attempt to characterise crack tip stress fields. The ability to apply two parameter fracture concepts to real engineering structures requires methods for calculating T for complex components with realistic semi-elliptical defects. A simple engineering method for achieving this was developed making use of linespring elements in the finite element package ABAQUS. This approach was validated by the calculation of T for semi-elliptical cracks at the chord-brace intersection of a tubular welded joint, modelled using the mesh generation program PATRAN. The micromechanics of cleavage, using the Ritchie-Knott-Rice model have also been constructed. This work relates the ratio of J for unconstrained and constrained geometries to critical microstructural distance, critical cleavage stress and the toughness ratio on the strainhardening effect. The elastic-plastic behaviour of short and deeply cracked bend bars has previously been described by Betegon and Hancock based on the first two terms of the Williams expansion. A local cleavage criterion has been applied to these fields to indicate the effect of loss of constraint on lower shelf toughness of shallow cracked bend bars. The work models the maximum temperature at which cleavage can occur in these geometries to show the effect of constraint and aJW ratio of cracked bend bars on the ductile-brittle transition temperature. This has also been backed by a significant experimental research program. Finally constraint dependent toughness has been considered in relation to failure assessment methodologies. A simple engineering method for modifying these Failure Assesssment Diagrams has been presented, this consists of considering the constraint matched toughness of the strucutre. This procedure recovers the original Failure Assessment Line and unifies the constraint dependent fracture toughness within defect assessment schemes which utilise Failure Assessment Diagrams.
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Richardson, James Bruce. "The mechanics of fracture healing." Thesis, University of Aberdeen, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290866.
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The mechanics applied to healing fractures vary widely. At one extreme rigid internal fixation is advocated, while at the other early mobilisation is recommended using external splints. Kuhn's method of paradigm orientated research was used to define the historical context of current assumptions regarding fracture healing. Conflict between the various schools of thought is the main evidence for failure of these assumptions and the need to evolve a new perspective on fracture healing. A paradigm is presented which proposes healing by external callus as an early stage and 'primary healing' as the later stage as of one continuous but changing process. A fundamental hypothesis was tested: that mechanics is the major control of fracture healing in man. A multicentre study of 102 patients with serious fractures were treated with external skeletal fixation. In 60 patients rigid external fixation was applied. In the remaining 42 the same fixation device was used, but adapted to apply 1 to 2mm of cyclic axial micromovement across the fracture. A piston applied 500 cycles of movement over a 30 minute period each day until this could be achieved by the patient on weight-bearing. Objective assessment required development of new techniques of measuring fracture stiffness and defining the point of healing. This objective measure, and clinically defined healing, were significantly faster in the group treated with micromovement (two-way analysis of variance, p = 0.005 and 0.03, respectively). Repeated injury by plastic deformation is proposed to maintain callus growth in the first phase of healing. Evidence for the required parameters of movement was gathered from the trial of micromovement, from measurements in 4 cases of epiphyseolysis and also 8 patients undergoing arthrodesis. It would appear appropriate to apply cyclic axial displacement of 2mm within the first two weeks from injury and of consistent direction until sufficient bulk of callus is formed. Thereafter axial compaction is appropriate in a second phase where callus matures. The mechanics that govern remodelling were considered to apply to the final phase. Failure of a cell culture model to display obvious results from cyclic loading may indicate that the response to mechanical loading is indirect. Intermediate and mechanically dependent biochemical and bioelectrical factors are discussed.
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Stehn, Lars. "Tensile fracture of ice : test methods and fracture mechanics analysis." Doctoral thesis, Luleå tekniska universitet, Byggkonstruktion och -produktion, 1993. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18394.
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This thesis is concerned with several aspects of fracture of both brackish (low salinity) sea ice and freshwater ice. The tests and analyses are confined to tensile, or in fracture mechanics language, Mode I, fracture. A large part of this thesis is dedicated to demonstrate that Linear Elastic Fracture Mechanics (LEFM) can be applicable on ice by laboratory and in-situ tests of defined specimens. All interpretations are made using the dicipline of LEFM.First, the development of a field test equipment called FIFT ( a Field Instrument for Fracture toughness Tests on ice) is described. The FIFT is used in both field and laboratory fracture toughness tests on brackish sea ice from the Gulf of Bothnia to describe porosity effects on the apparent fracture toughness, KQ, and estimate crack velocities. An appropriate speciment size, in terms of notch sensitivity, is then provided valid for grain sizes ranging from 1.6 to nearly 100 mm.An augmented use of the FIFT is then described where fracture toughness tests are performed on S1 type freshwater ice to investigate if similarities exist in the local KI fields for three different fracture geometries. The results indicate that, under comparable conditions, KQ is similar for all of the geometries. However, the type of specimen, has a marked influence on the character of the fracture surface.Then, the influence of structural anisotropy on the fracture toughness of S1 ice is investigated by fabricating and testing three different fracture geometries from a single ice core. This approach is suitable for both field and, as in this work, laboratory studies. There is a wide scatter in the KQ values. Possible explanations to the results are discussed in terms of the microstructural influences and specimen size effects.Finally, crack growth resistance measurements on large grained S1 ice is conducted. A new fracture geometry is used which is found to be extremely favorable of promoting stable, stick-slip, crack growth over a large portion of the uncracked ligament. Now a complete characterization of the fracture resistance curve is therefore possible, A negative fracture resistance KR-curve is evaluated for the S1 ice at -16°C.Godkänd; 1993; 20070426 (ysko)
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Tiernan, Declan Martin. "Collocation studies in fracture mechanics and quantum mechanics." Thesis, Queen's University Belfast, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318739.
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Gerde, Eric Stendahl. "Fracture and friction /." Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3008334.
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Okada, Hiroshi. "Boundary element methods for linear and nonlinear solid mechanics problems : and fracture toughness enhancement mechanisms in ceramic materials." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/19169.
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Arteaga-Gomez, Joaquin M. "Development of crack generation and propagation algorithms for computational structural mechanics." Fairfax, VA : George Mason University, 2009. http://hdl.handle.net/1920/3430.
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Thesis (M.S.)--George Mason University, 2009.Vita: p. 64. Thesis director: Rainald Löhner. Submitted in partial fulfillment of the requirements for the degree of Master of Science in Computational Sciences. Title from PDF t.p. (viewed June 10, 2009). Includes bibliographical references (p. 60-63). Also issued in print.
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Zhang, Chengjie. "Fracture mechanisms in wood fibre reinforced polyethylene." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq41584.pdf.
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Yin, Xiaochen. "Concrete fracture process zone characteristics /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/10183.
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Hauch, Jens Andreas. "Dynamic fracture in brittle materials /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Pollitz, Ernest Theodore. "Studies on elastic-plastic fracture mechanics." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/18363.
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Vasic, Svetlana. "Applications of fracture mechanics to wood." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0030/NQ65471.pdf.
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Ohlsson, Ulf. "Fracture mechanics analysis of concrete structures /." Luleå, 1995. http://epubl.luth.se/avslutade/0348-8373/179/index.html.
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Carling, Michael John. "Fracture mechanics of short fibre composites." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/46986.
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Quintana, Alonso Ignacio. "Fracture mechanics of brittle lattice materials." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611458.
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Karstensen, Annette Degn. "Constraint estimation schemes in fracture mechanics." Thesis, University of Glasgow, 1996. http://theses.gla.ac.uk/7228/.
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Elastic-plastic crack tip constraint has been estimated for the common planar crack geometries. These include single edge cracked bars in tension and bending, centre cracked panels, and double edge cracked bars. The description of the stress field has been modified from a one parameter characterisation, based on K or J, to include a second term. The second parameter is a non-singular term, described either in terms of an elastic T-stress or a Q field. The limits of one and two parameter characterisation are discussed for single edge bars in tension and bending and for centre cracked panels. For the single edge geometries the two parameter characterisation was found to extend the characterisation well beyond the one parameter approach. For the centre cracked panels the two parameter characterisation in terms of a J-Q approach was found to be more accurate than a J-T approach at high levels of deformation. For the single edge cracked bending and tension geometries the second parameter Q is divided into two components named QT and QP. QT is an elastic term which depends on the elastic T stress and is independent of the distance from the crack tip. The second component, QP, arises from global bending on the uncracked ligament. This is a distance dependent term which depends on the level of deformation and can either be expressed as a function of the load normalised by the limit load or as a function of the plastic component of the J-integral. For single edge bend bars the constraint estimation provides a basis for a method of predicting fracture toughness using local failure approach, where the failure criterion is expressed in terms of the stress level ahead of the crack tip. Finally the constraint of mixed mode problem has been analysed and compared with that of pure Mode I problems.
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Kasturi, Krishna Kumar. "Microcracking Fracture Toughness for Graphite Epoxy Composite Laminates Using Finite Fracture Mechanics." ScholarWorks@UNO, 2006. http://scholarworks.uno.edu/td/427.
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Graphite/epoxy composite laminates are widely used in the aerospace industry. However the industry cannot take full advantage of the superior strength and stiffness of composite materials until their failure mechanisms can be thoroughly understood by engineers. Recognizing the importance of such understanding, the current study was undertaken to determine the microcracking fracture toughness in composite laminates using the energy release rate criteria. Three materials of specific interest in the aerospace industry – IM7/977-2, IM7/5555 and IM7/5276-1 – were analyzed. To evaluate the microcracking fracture toughness, displacement controlled static tensile tests were performed. Microcrack density (the number of microcracks per unit length) was measured as a function of applied stress. The data were analyzed to obtain the microcracking fracture toughness (Gm) for each material system. The value of Gm can be used to predict the microcracking behavior of composite laminates made from the corresponding material.
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Zhang, Wenbing. "A method and program for quantitative description of fracture data and fracture data extrapolation from scanline or wellbore data /." May be available electronically:, 2001. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Davis, Michael Woods. "Thermally induced fast fracture /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487262825077516.
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Everett, Kay Dee Furman. "Mechanisms and Implications of Fracture in Cardiovascular Stents." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11458.
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Cardiovascular stents are one of the most widely implanted medical devices, with over 1 million implanted each year in the United States alone. While stent failure modes of restenosis and thrombosis have been widely examined, there is an increasing appreciation of the propensity for stents to fracture and break after implantation. It remains unclear however what causes these fractures, which patients and devices are most susceptible, and whether fracture results in failure of device function.Engineering and Applied Sciences
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Tombs, Helen Charity. "Fundamental mechanisms of fracture and liberations of minerals." Thesis, University of Exeter, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264611.
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MuratoÄ, lu Orhun Kamil. "Toughening and fracture mechanisms of rubber modified polyamides." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11483.
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Li, Jian Xing. "Ductility and fracture mechanisms of particulate filled thermoplastics." Case Western Reserve University School of Graduate Studies / OhioLINK, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1060703053.
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Kumar, Akshay. "Low temperature fracture mechanisms in spheroidised ferritic steels." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491508.
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Low temperature fracture mechanisms of annealed (40h at 650°C) A533B (spheroidised ferritic) steel and heat-treated (lh at 316°C) 4340 (spheroidised ferritic) steel were investigated. Uniaxial tensile tests over the temperature range of -190°C to 60°C were used to identify crack nucleation sites, whether these cracks nucleate at early stages of loading or just prior to fracture, and whether crack growth is continuous. Additionally, electron probe microanalysis and electron back scattered diffraction were used to characterise fracture nucleation sites and microcracks in annealed A533B steel; and Charpy impact tests and electron probe microanalysis were used to investigate fracture nucleation site properties in heat-treated 4340 steel. These results were then compared with the low temperature fracture mechanisms observed in as-received bainitic A533B steel. This study found that at the lowest test temperatures both spheroidised A533B steel and heat-treated 4340 steel fail by 'quasi-cleavage' while as-received A533B steel fails by 'true transgranular cleavage'. Quasi-cleavage fracture surfaces are characterised by voids separating planar facets. Unlike in true transgranular cleavage, quasi-cleavage fracture is preceded by significant plastic deformation even at the lowest test temperatures. This study also found that fractured brittle second phase particles played no role in fracture nucleation in both the heat-treated steels. In heat-treated 4340 steel, fracture nucleated at a localised region of microvoids. In spheroidised A533B steel, 3 types of nucleation sites were seen: (a) a single void smaller than 2.5 J.lm in diameter, (b) single voids larger than 2.5J.lm in diameter and (c) a region of microvoids in a sulphur-rich area.
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O'Brien, James F. "Graphical modeling and animation of fracture." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/13074.
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Jeang, Fure Lin. "Non-linear analysis of concrete fracture /." Thesis, Connect to this title online; UW restricted, 1985. http://hdl.handle.net/1773/10133.
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Luckyram, Jeenarainsingh. "Fatigue and fracture of structural adhesives." Thesis, University of Dundee, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240139.
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Chen, Zhong. "Electroplastic fracture propagation in cantilever beams." Thesis, University of Reading, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339516.
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Gagnepain-Beyneix, Jeannine. "Etude experimentale des tremblements de terre : exemple de la region d'arette (france)." Paris 7, 1987. http://www.theses.fr/1987PA077010.
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La localisation des seismes enregistres permet de mettre en evidence une fracture crustale majeure, situee a la bordure nord de la haute chaine et qui pourrait correspondre a la suture des plaques europe et iberie. L'etude des mecanismes au foyer et les resultats de la geodesie montrent une elevation de la haute chaine par rapport a l'avant pays nord. L'examen des parametres de la source montre l'heterogeneite de l'etat de contrainte a la surface de la faille sismique. L'etude de l'attenuation des ondes sismiques ne revele pas de variation du facteur de qualite du milieu liee a l'activite sismique. Ces resultats permettraient de progresser dans les domaines de la sismogenese et de la prevision sismique dans les regions de sismicite moyenne
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Dhansay, Nur Mohamed. "Fracture mechanics based fatigue and fracture toughness evaluation of SLM Ti-6Al-4V." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/24326.
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The focus of this research project was to determine experimentally the fatigue and fracture toughness characteristic, from a fracture mechanics perspective, of Ti-6Al-4V titanium alloy manufactured by Selective Laser Melting (SLM). Three build orientations are considered where a fatigue crack is grown parallel and two are grown perpendicular to the build orientation. The project then endeavours to generate a fracture mechanics based Paris equation from the fatigue crack growth rate results and together with the fracture toughness, fatigue life predictions may be determined based on crack propagation lifetimes. SLM is an Additive Manufacturing (AM) technique whereby an object is fabricated in a layerwise manner via the use of lasers, directly from a 3D CAD model. This process allows for the manufacture of complex designs in its net or near net shape form, which is not possible with conventional manufacturing techniques. There are minimal amounts of material wastage and it potentially eliminates post manufacture machining and processing costs. Ti- 6Al-4V is used in many applications where high strength at low density is required at moderate temperatures. Corrosion resistance qualities of the alloy are also considered for many applications. Some of the applications where this alloy is used include turbine engine components, aircraft structural components, aerospace fasteners, high-performance automotive parts, marine applications, medical implant devices and sports equipment. Due to the large use of the alloy in industry and with the potential benefits of manufacturing by SLM, there is a great need for investigating SLM Ti-6Al-4V as a viable alternative to conventional casting, forging and machining. There is limited literature covering the fatigue crack growth rate and fracture toughness of SLM Ti-6Al-4V and the effect of build orientation on these characteristics. However, it is clear, from the limited available literature that fatigue crack growth rate behaviour is affected by build orientation, and so this project investigates the effect of these orientations, and aims to contribute to understanding why these orientation effects occur. Since there is even less literature available on the fracture toughness of SLM Ti-6Al-4V with respect to build orientation, this project also endeavours to characterise orientation effects on fracture toughness, if any, and compares these with those of conventionally manufacture Ti-6Al-4V.
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Averett, Rodney Dewayne. "Fracture Mechanics of High Performance Nylon Fibers." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5238.
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A fracture mechanics protocol appropriate for small fibers (35 micron diameter) is presented, which allows for the determination of the strength limitations of high performance nylon 6,6 fibers. Specifically, linear elastic fracture mechanics (LEFM) techniques are employed in addition to elastic-plastic fracture mechanics (EPFM) theories to achieve this.
We assume that a minute semi-elliptical flaw of an unknown size exists in the specimen, as a result of the detrimental effects of the manufacturing process (melt spinning). Next, we seek to propagate this flaw in a stable manner through an ancillary process such as high cycle or low cycle fatigue (load-unload). After propagation, uniaxial tensile experiments are performed on the fatigued samples, by which the crack growth eventually becomes catastrophic during the process. After performing scanning electron microscopy (SEM) techniques and reviewing fractography, we are able to determine the critical flaw size and ligament length that leads to unstable crack propagation. These results are substituted into the appropriate LEFM equations and are in close agreement with material properties for nylon 6,6. A discussion is provided that draws parallel to the topics discussed in the literature investigation and the experimental results of this study.
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Sticko, Simon. "Smooth Particle Hydrodynamics Applied to Fracture Mechanics." Thesis, Uppsala universitet, Tillämpad mekanik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-202881.
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A numerical method commonly referred to as smooth particle hydrodynamics (SPH) is implemented in two dimensions for solid mechanics in general and fracture mechanics in particular. The implementation is tested against a few analytical cases: a vibrating plate, a bending plate, a modus I crack and a modus II crack. A conclusion of these tests is that a better way of treating a shortcoming of SPH called tensile instability is needed. A study is made on the best choice of a vital parameter called the smoothing radius, and it is found that a good choice of the smoothing radius is roughly 1.5 times the initial particle spacing.
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Hosseini, Seyed Mehran. "Hydraulic fracture mechanism in unconsolidated formations." Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-08-6390.
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Most models developed for hydraulic fracturing in unconsolidated sands are based on Linear Elastic Fracture Mechanics (LEFM) and tensile fracture (Mode I fracture). However, in unconsolidated sand formations the field data shows that LEFM based models cannot properly predict the fracture behavior. Hydraulic fracture lab experiments in a true triaxial setup which was made as a part of this study are designed to investigate the failure mechanism around the crack tip in unconsolidated sands and effects of fluid rheology, leak off, and stress state are investigated. The results show that two mechanisms of tensile and shear failure are involved in fracture propagation in unconsolidated sands and depending on the fracturing fluid rheology and stress state of the formation one or both of them can happen at the crack tip. Several experiments with different fracturing fluids, rates, and different stress boundary conditions are categorized into two major categories based on whether we have a fracture or not. A subsequent categorization is used to categorize the fractured cases into Tensile Failure, Shear Failure and Mixed Failure categories. First the experimental observations are presented and subsequently observations are analyzed and compared in order to explain the observations and conclusions. ;Tensile failure category is happening in medium viscosity fracturing fluids in the order of 20,000 cP viscosity at unit 1/s shear rate. Shear failure category is mostly taking place in low viscosity fluids (200 cP viscosity at unit 1/s shear rate). Mixed mode fracturing is happening in high viscosity fluids (70,000 cP viscosity at unit 1/s shear rate) with high stress anisotropy. However, the same fluid will give a No Fracture result in the case of isotropic or near isotropic stress state. It is shown that higher stress anisotropy increases the tendency of shear failure and at the same time, the resulting fracture will propagate in a preferential direction. However, tilting and branching might happen due to high stress anisotropy which is more pronounced in case of thicker fluids. It was also observed that in case of vaseline injection, stress anisotropy decreases treatment breakdown pressure.text